The elevators may not be moving equally. Even though they are connected by a rod they may not be equal.Especially if when they were glued together they were not weighted down on a flat surface. The epoxy during the drying process can introduce a warp.

Easy to find out. Take a long straight piece of balsa and tape it to the top of one elevator, take another straight stick of balsa and tape it to the other elevator. Both sticks should be pointing towards the rudder to the point where the meet right behind the rudder.

The sticks should line up and stay lined up all the way through the range of travel

As others have said rolling left could very well be you need right thrust.

I have even seen a misaligned rudder cause this